Security inspection is of great importance in fields such as anti-terrorism and fighting against trafficking in drugs and smuggling. After 9/11 terrorist attacks of the United States, people more and more emphasize security inspection of civil aviation. As the fighting against trafficking in drugs and smuggling is deepened, the requirement for inspection of aviation containers and luggage carried by railway becomes higher and higher.
At present, X-ray radiation imaging apparatuses are mostly used as security inspection apparatuses for use at airports, railway or highway transportation. Perspective imaging stands prominent in the art of radiation imaging. The biggest drawback of perspective imaging system lies in failure to solve the problem of overlapping of images of the object in the direction of rays and failure to achieve 3-dimensional inspection.
For example, if a plastic explosive is produced in the shape of thin sheets and sandwiched in a bulky object, when the thin sheets are parallel to the conveyance belt of the perspective imaging system, i.e., are disposed as being vertical to the X-ray sector, it is very difficult to observe presence of the thin sheets on the acquired images.
As technology develops, computed tomography (CT) imaging technology gradually becomes mature and has already been applied to luggage inspection systems. Inspecting luggage by a CT system requires rotational scanning and reconstructing a 3-dimensional image using the scanning data. In particular, as far as a spiral CT system is concerned, relative rotation and translation is carried out between a radiation source and an inspected object so that the radiation source has a spiral movement trajectory relative to the inspected object. In the prior art spiral CT systems, a radiation source moves spirally relative to the inspected object with a small pitch so as to obtain scanning data (i.e., high-precision scanning data or complete scanning data) of all slices of the inspected object. As a result, the inspection speed of such a spiral CT system is generally very slow so that a great deal of time is spent in a conventional inspection. However, at present security inspection systems in aviation, railway or highway transportation generally requires on-line full-time inspection and articles need to be quickly inspected. Very apparently, the scanning speed of the prior art spiral CT systems cannot meet the requirement for inspection speed. Certainly, increase of the scanning pitch of the spiral CT system will improve the scanning speed and thereby improve the inspection speed. However, increase of the pitch will reduce scanning precision and thereby reduces precision of the reconstructed 3-dimensional image and thereby reduces accuracy in inspection of cargo.